1. Field of the Invention
The invention relates to an assembly of a pneumatic tire and a rim, a pneumatic tire and a rim for holding the tire.
2. Related Art Statement
FIG. 1(a) schematically shows a shape of a pneumatic tire 41 of a prior art. As shown in FIG. 1(a), the tire 41 takes its maximum width at a circumferential cross section “T” with respect to the wheel center axis and located in the central portion of the tire. Such conventional tire 41 has two side portions 45 whose radii of curvature are smoothly changed, thereby causing a side tension due to internal pressure of air in the tire. The tire has two bead portions 43 embedded within the end portions 41a thereof. The end portions 41a of the tire 41 were fixed on a rim 42.
As generally understood, a low rolling resistance may be obtained by using a tire with a large value of Tb/Ts, provided that Tb is a belt tension and Ts is a side tension of a tire due to internal pressure of air inflating the tire. In other words, a tire with a high belt tension and a low side tension may be preferably used for reducing the rolling resistance of the tire.
The reasons will be described. An angled belt layer generally used in a conventional radial-ply tire has cross layers and rubber layers sandwiched between the cross layers. The roundness of the belt layer of a tire can be maintained in the region of the tire contacting the ground when the tire rolls on the ground under a load, by improving the belt tension. When the roundness of the belt layer is maintained, the bending deformation of the belt layer from a round shape toward a flat shape is relatively small. Such small bending deformation results in a small shear strain deformation occurred within the rubber layers between the cross layers of the angled belt layer. The shear strain deformation of the rubber layer between the cross layers results in a delay of stress transmission in the rolling tire, due to the viscoelasticity of the rubber layer or the adjacent rubber portion. The delay is one of causes of an increased rolling resistance.
One solution for reducing the rolling resistance is to maintain the roundness of a belt layer when a tire is rolling. Clearly, it is thus preferable to improve Tb and reduce Ts for realizing such deformation preserving the roundness.
Many researches have been conducted for adjusting the cross sectional design of a tire so that a high Tb and low Ts may be realized. For example, a Japanese Patent application publication “Kokai” number 079402/1977 discloses a proposed cross section of a tire for achieving such adjustment.
This publication number 079402/1977 discloses a wheel with a pneumatic tire having tire beads, in which the width of the tire is its maximum near the tire beads.